The present invention relates to holographic recording and more especially to a method and apparatus for holographically recording a plurality of holograms upon the same position of a recording material.
In known methods for recording several holograms on top of each other, the recording of the holograms is carried out at different azimuth angles. The azimuth angle is defined as being the angle between the plane defined jointly by the reference beam and the object beam, and a straight line which is stationary on the recording material.
There are two possibilities for changing the azimuth angle when making recordings on top of each other, i.e., changing it with respect to one and the same recording material. The simplest possibility is to rotate the recording material through the azimuth angle desired. This rotation is carried out around a straight line which is at a right angle with the recording material. Alternatively, it is also possible to fix the recording material and rotate the optical elements. Finally, there is the possibility of fixing the recording material and the light source, and then rotating the beam splitter of a known recording apparatus.
German Offenlegunsschrift No. 2,253,413 relates to a device and a method for recording of several holograms on top of each other while the azimuth angle is changed. In the disclosed method the rotation of the polarization direction is kept constant by means of circular polarizers so that, because of the strength of the reflection which depends on the polarization direction, no recording differences occur.
These methods and devices for the superposition of holograms by changing the azimuth angle have a common disadvantage. All these methods require mechanical movement of either the optical elements or the recording material. Due to this mechanical movement, both the access time and the change-over time from one azimuth angle to another are very long, and therefore the application of this recording technique is unsuitable for all the problems which require the change-over to be as quick as possible.